This invention relates to a freeze preventing valve which can prevent itself from freezing even if the valve is used in a cold district.
A room heater for a Diesel locomotive which travels in a cold district, for example, adopts in general a steam heater in view of structural and economical considerations. In this structure, valves for exhausting condensed water of steam are mounted at a predetermined interval at the suitable positions of a steam feed pipe. A valve of this type has heretofore been constructed, as shown in FIG. 1, to have a valve housing 2 connected to a steam feed pipe 1, an exhaust port 3 formed at the lower part of the housing 2, a valve element 4 disposed in the exhaust port 3 for opening or closing the exhaust port 3, a guide rod 5 for movably supporting the shaft 4a of the valve element 4, a valve body 6 for holding the rod 5 at the top thereof, and stainless bellows 7 disposed between the collar 5a of the rod 5 and the valve element 4. When the interior of the housing 2 is maintained by the stream at a high temperature, gas in the bellows 7 is heated and expanded to cause the bellows 7 to be elongated as shown in FIG. 1, thereby moving downwardly the valve element 4 to automatically close the exhaust port 3. Thus, when the steam is partly cooled to produce condensed water, which then flows into the housing 2 to thereby cool the bellows 7 through the pipe 1, the bellows 7 are contracted to move upwardly the valve element 4, with the result that the valve element 7 automatically opens the exhaust port 3. In this manner, the condensed water is naturally exhausted externally from the exhaust port 3 through a plurality of holes 6a perforated at the wall of the valve body 6.
Since the bellows 7 for automatically moving the valve element 4 upwardly or downwardly due to the temperature difference is, however, constructed to fill and seal the gas therein to be expanded as described above, the bellows 7 are affected by the influence of the fatigue of repeated elongations and contractions for a long period of time, and develop fine cracks, causing a gas leakage or improper opening or closing of the valve. Thus, the condensed water is concentrated in the valve housing in winter, the valve itself is thus frozen, and the valve housing is then damaged. Therefore, in order to protect against the freezing of condensed water in the valve a preliminary valve 8 is opened to discharge the condensed water, or the valve body is formed in a lateral type. However, this does not overcome the above-described drawbacks. To prevent the freeze of the valve of this type, it is necessary to check and maintain, and replace the bellows, and to provide a remedy of preventing the damage of the bellows themselves, i.e., the improvement of the durability in period and the reduction in the manufacturing cost.